1. Field of the Invention
The present application relates to an image reading device in which a line sensor reads an image of a document by moving along a transparent member, which defines an image reading area, in a direction perpendicular to a reading line of the line sensor.
2. Description of Related Art
A flatbed scanner is known as an image reading device that reads an image of a stationary document. A line sensor of the flatbed scanner reads an image of a document placed on a contact glass while reciprocating along the contact glass.
The contact glass may be bent when an external force is applied, such as a pressing force of a document against the contact glass. The bending of the contact glass may cause (1) deterioration in quality of a image read by the line sensor, (2) a collision between the contact glass and the line sensor, or (3) a breakage of the contact glass.
To address the foregoing problems, several structures have been proposed for an image reading device. JP2001-235814A discloses a structure in which a rigid reinforcing frame and a dolly plate are disposed under a contact glass, and the distance between the reinforcing member and the dolly plate are adjusted using screws to correct the bend of the contact glass.
JP2001-203841A discloses a structure in which a contact glass is previously bent with respect to the sub-scanning direction of a line sensor, and the line sensor is moved while being urged toward the contact glass. Accordingly, the bending of the contact glass with respect to the main scanning direction is lessened, and the distance between the line sensor and a document is kept uniform.
JP8-228266A discloses a structure in which a middle part positioning member is provided in a support member for the line sensor. The middle part positioning member supports a contact glass being bent, thereby reducing the deviation in the focal depth of the line sensor.
However, in the structure disclosed in JP2001-235814A, the dolly plate supports only the center of a side of the contact glass, and thus the contact glass is likely to be bent at a corner portion thereof.
In the structure disclosed in JP2001-203841A, if a rigid document is placed on the previously bent contact glass, the document may float with respect to the sub-scanning direction. Or, if a document cover, when closed, does not conform to the contact glass, ambient light may enter the inside of the image reading device.
In the structure disclosed in JP228266A, because the middle part positioning member contacts a document reading area of the contact glass, the document reading area may be soiled. The middle part positioning member supports the contact glass by making a point contact with the contact glass. Thus, the load due to an external force may be applied intensively to a contact point, causing a breakage of the contact glass.
Therefore, a need has arisen for an image reading device that can maintain the quality of an image read by a line sensor even when an external force is applied to a contact glass.